The invention relates to a percussion device comprising a body and therein a percussion piston that moves longitudinally in a reciprocating manner by action of pressure fluid, in the body a first and a second pressure fluid space in the rear end and correspondingly in the front end of the percussion piston and a control valve that is substantially sleeve-like, locating around the rear end of the percussion piston and movably mounted in the longitudinal direction of the percussion piston, as well as pressure fluid channels for feeding pressurized pressure fluid in and out of the percussion device.
In pressure-fluid-operated percussion devices the reciprocating percussion movement of the percussion piston is controlled by a control valve that controls pressure fluid feed onto pressure surfaces of the percussion piston. In a known solution the control valve is located axially to the percussion piston in the rear end of the percussion piston. The position of the control valve in various stages of percussion is controlled by the position of the percussion piston with respect to the percussion device, and consequently as the percussion piston approaches its rear position it causes a change in the position of the control valve, typically by means of external pressure control or forced control by the effect of an increase in the pressure of the pressure fluid in a substantially closed space provided in the rear space of the piston. In the external pressure control, as the position of the percussion piston changes during the reverse stroke the percussion piston lets pressurized pressure fluid act on the control valve, which makes the control valve move from one position to another. In the forced control, a pressure rise in the rearmost pressure fluid space, in turn, results from the percussion piston compressing the pressure fluid while penetrating into the rearmost pressure fluid space, which is rendered substantially closed by the position of the percussion piston during the reverse stroke.
The external pressure control poses a problem that the valve moves slowly from one position to another. In the forced control solution, in turn, the position change of the valve is fast, but a problem is that the valve has a high final speed in both extreme positions of its movement. In addition, the pressure fluid in front of the valve flows directly into a tank, which decreases efficiency.